The purpose of this NIMH-sponsored pilot study is to collect information on the efficacy and safety of drug treatments for children and adolescents who suffer from both ADHD and anxiety disorders. Specifically, the study will examine the benefits of the stimulant medication both alone and in combination with fluvoxamine, a selective serotonin reuptake inhibitor (SSRI) that has antianxiety effects. Young people aged 6 to 17 diagnosed with these co-occurring disorders may be eligible to participate.